tips

Adding a signature to your picture. Open a picture in Preview and click Tools->Annotate ->Signature ->Manage Signature.
Follow the on-screen instructions to add a signature. You can save your signature for future use as well.

You can get exchange rate and convert currency with Spotlight in El Capitan. The currency conversions are done with Calculator app by gathering exchange rates from Yahoo, but the data is obviously aggregated into Spotlight for convenience.

Built-in emoji Press ctrl +⌘ + space to open the window. This window contains an exhaustive list of special characters. You can choose the special characters and emoticons that you need from this window.

Speech to text conversion you can convert your speech-to-text by pressing the function (fn) key twice and begin speaking. Your voice gets converted to text when you press function (fn) key one more time. The OS X types out as you speak.